Optical disk and optical disk fabrication method

ABSTRACT

An optical disk fabricating method, optical disk, and optical disk apparatus, which provides effective use of a disk&#39;s information recording surface and allows for high density recording. The invention implements land/groove recording, the width of lands and grooves being approximately equal and the track pitch being set to approximately 0.5 μm. A disk fabricated according to the invention includes a light transmission layer having a thickness of approximately 100 μm.

BACKGROUND OF THE INVENTION

This invention relates to an optical disk fabricating method, opticaldisk, and optical disk apparatus, and more particularly, to thefabrication, recording and reproduction of optical disks that have beenformed according to the so-called land/groove technique.

Currently, the DVD (Digital Versatile Disc) is being proposed as anoptical disk apparatus for recording information at high density. TheDVD is designed to be able to record 2.6 GB of data on a single side,the recording being performed by irradiating a laser beam having awavelength of 650 nm onto an optical disk through an optical systemhaving a numerical aperture of 0.6. Using this technique, about onehour's worth of image signals can be recorded on a single side of adisk.

However, a typical home video tape recorder (VTR) has a basic recordingtime of two hours. Thus, in order for DVD's to become a viablesubstitute for VTRs, they must be provided with the capability to storemore data. For example, although editing or the like can be performed byeffectively using the characteristic functions of optical disk such asrandom access, about three hours' worth of image signal must be recordedin order to make DVDs desirable. In the case of a DVD system, a threehour recording time means that the disk should be capable of storingabout 8 GB of data.

For this reason, it is necessary to make effective use of theinformation recording surface of an optical disk.

SUMMARY OF THE INVENTION

The present invention has been made with the above points in mind.Accordingly, an object of the invention is to provide an optical diskfabricating method, optical disk, and optical disk apparatus whichpermit effective use of the information recording surface of the disk,thereby allowing data to be recorded at higher density than before.

A technique for fabricating an optical storage disk according to theinvention involves providing a base disk having a transparent layer anda recording layer, the transparent layer having a thickness between 10μm and 177 μm; and irradiating the base disk with a laser beam so as toform a multiple of recording tracks on the recording layer, the tracksbeing substantially concentric about the center of the base disk, havinga track pitch of 0.64 μm or less, and alternating radially between landtracks and groove tracks, wherein each land track is located on thesurface of the recording layer and each groove track is located within agroove on the surface of the recording layer.

When the invention is applied to an apparatus accessing the type ofoptical disk described above, groove tracks and land tracks are accessedby irradiating the laser beam onto the disk via an optical system havinga numerical aperture of 0.78 or more with a working distance being setto 560 μm or less. The rotation speed of the optical disk may beswitched in stages from the inner circumferential side to outercircumferential side of the optical disk by noting the irradiationposition of the laser beam.

Forming the light transmission layer with a thickness of 10 μm to 177 μmallows an optical system having a high numerical aperture to read datafrom the disk; and data can be recorded at high density. By spirallyforming tracks with a pitch of 0.64 μm or less on the informationrecording surface, the information recording surface can be effectivelyused, thereby helping to improve recording density. Recording densitymay be further improved by ensuring that the width of a groove and thatof a land are equal or almost equal.

In the optical disk apparatus of the invention, the recording densityadvantages of the above-described disk are realized by accessing groovetracks and land tracks. Moreover, by switching the rotation speed of theoptical disk in relation to the radial position of the irradiatinglaser, additional recording density advantages may be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view provided for explanation of zone recording by amastering apparatus according to a first embodiment of this invention.

FIG. 2 is a block diagram showing a mastering apparatus applied to zonerecording in FIG. 1.

FIGS. 3A to 3C2 are schematic diagrams showing the configuration of asector as depicted in FIG. 1.

FIG. 4 is a perspective view of an optical disk produced by themastering apparatus in FIG. 1.

FIG. 5 is a block diagram showing an optical disk apparatus foraccessing an optical disk produced by the mastering apparatus in FIG. 1.

FIG. 6 is a schematic diagram showing the optical head of the opticaldisk apparatus in FIG. 5.

FIG. 7 is a schematic diagram showing the configuration of an objectivelens of the optical head in FIG. 6.

FIG. 8 is a block diagram showing a data processing system of theoptical disk apparatus in FIG. 5.

FIG. 9 is a drawing used for explanation of sector structure in theoptical disk as employed in the apparatus of FIG. 8.

FIG. 10 is a drawing showing an ECC block in the optical disk asemployed in the apparatus of FIG. 8.

FIG. 11 is a drawing used for explanation of frame structure in theoptical disk as employed in the apparatus of FIG. 8.

FIG. 12 is a plan view used for explanation of processing of continuousdata in the optical disk apparatus in FIG. 8.

FIG. 13 is a plan view used in comparison with FIG. 12 to explainprocessing of continuous data in an optical disk apparatus according toa second embodiment of this invention.

FIG. 14 is a plan view used for explanation of sectors formed by amastering apparatus according to yet another embodiment of thisinvention.

FIG. 15 is a plan view used for explanation of sectors formed by amastering apparatus according to a still further embodiment of thisinvention.

FIG. 16 is a plan view used for explanation of sectors formed by amastering apparatus according to an additional embodiment of thisinvention.

FIG. 17 is a plan view used for explanation of processing of continuousdata in the optical disk apparatus applied to the optical disk depictedin FIG. 16.

FIG. 18 is a plan view used for explanation of sectors formed by amastering apparatus according to a further embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 2 is a block diagram showing a mastering apparatus according to afirst embodiment of the present invention. In the optical diskfabricating process of this embodiment, a source disk 2 is exposed tolight by the mastering apparatus 1 and an optical disk is produced fromthe source disk 2.

In the mastering apparatus 1, the source disk 2 (e.g. a glass platecoated with a resist) is rotationally driven at a constant angularvelocity by a spindle motor 3.

An optical head 4 irradiates a laser beam L onto the source disk 2 asthe head is moved by a sled mechanism from the inner circumferentialposition to the outer circumferential position of the source disk 2.Irradiating the disk in this manner, as the disk rotates, allows theoptical head 4 to form spiral tracks which run from the innercircumferential position to the outer circumferential position of thesource disk 2. The optical head 4 is controlled by the sled mechanism tomove in the radial direction by about 1.0 μm per rotation of the sourcedisk 2 so that tracks are formed with a track pitch of 0.5 μm in thecase of land/groove recording. For comparing purposes, it is noted thatin the case of DVD land/groove recording, the track pitch is 0.74 μm.

In the system of FIG. 2, the mastering apparatus 1 can record data onoptical disks produced from the source disk 2 at a track recordingdensity of about 0.21 μm/bit. An expression relating the recordingdensity of an optical disk produced from source disk 2 and a DVD disk isshown below.

    4.7×0.74×0.267/(0.5×0.21)                (1)

In the above expression, the number 4.7 is the recording capacity (GB)of DVD and the numbers 0.74 and 0.267 are the track pitch (μm) and trackrecording density (μm/bit) of DVD, respectively. The numbers 0.5 and0.21 are the track pitch (μm) and track recording density (μm/bit),respectively, of a disk produced from source disk 2. Accordingly, theexpression (1) shows recording density according to the FIG. 2embodiment when the same data processing as for DVD is performed. Thevalue of the expression is >8 GB, and thus a disk produced from sourcedisk 2 can record more than 8 GB of data.

The optical head 4 sets the spot diameter of laser beam L so that, whenoptical disks are produced from the source disk 2, the grooves formed byexposure to laser beam L and the lands between adjacent grooves arealmost equal in width. The spot shape and light quantity of the laserbeam are set so that the effective exposure area of the beam is about120% of the desired groove width. In this manner, the optical head 4exposes the source disk 2 to the laser beam such that the resultingoptical disks are capable of land/groove recording.

Further, the optical head 4 is constructed so that it is movable in theradial direction of the source disk 2.

A drive circuit 5 drives the optical head 4 in response to a drivesignal SD. The drive circuit 5 switches the conditions of driving theoptical head 4 according to the position of the irradiating laser beamand the rotation of the source disk 2, thereby generating a zoned sourcedisk 2 as shown in FIG. 1. FIG. 1 provides a detailed view of a portionof the zoned disk showing the lands, grooves and pits.

The mastering apparatus 1 forms tracks on the source disk 2 so that anarea of 24 to 58 mm in radius is allocated on the information recordingsurface of an optical disk that is 120 mm in diameter. Furthermore, thedrive circuit 5 switches the conditions of driving the optical head 4 sothat the information recording surface is split into circumferentialareas referred to as sectors. Further, by changing the switching timingin stages from the inner circumferential track to the to outercircumferential track of the disk, the information recording surface isconcentrically split into a multiple of radial zones (Z0 to Zn).

With this construction, nine sectors are formed per track in theinnermost zone Z0 and the number of sectors per track increases by oneeach time there is a shift from one zone to its neighboring outer zone(e.g. from Z0 to Z1).

An enlarged view of a sector boundary (e.g. boundary associated witharrow A or B) is provided in FIG. 1. As can be seen, the leading portionof a sector is allocated in address area AR2 and the remaining area (or"user area") is allocated in area AR1. The drive circuit 5 radiallyshifts the position of the laser beam in the user area AR1 according tothe drive signal SD under control of a system control circuit (notshown), thereby forming wobbled grooves in the user area AR1.

The shifting of the laser beam position is suspended in the first halfof the address area AR2 and the light quantity from the laser beam isincreased intermittently by the drive signal SD to form a pit train onthe center of a groove track. In the second half of address area AR2,the laser beam position is shifted to the center of an inner land trackand the light quantity from the laser beam is increased intermittentlyby the drive signal SD to form a pit train on the center of the landtrack.

With this construction, the drive circuit 5, in the first half ofaddress area AR2, records the address data of a following groove sectoron a corresponding track center by a pit train, and in the second halfof address area AR2, the drive circuit records the address data of afollowing inner land sector on a corresponding track center by a pittrain.

When optical disks are produced from the source disk 2, the drivecircuit sets the light quantity of the laser beam such that the depth ofpit and groove is 1/6 to 1/5 of the 650-nm wavelength of laser beam.Grooves are formed so that the wobbling anplitude is 15 to 30 nm.

A wobble signal generating circuit 7 (FIG. 2) outputs a wobble signal,WB, which is a sinusoidal signal having a frequency which is synchronouswith the rotation of the source disk 2. The wobble signal generatingcircuit 7 outputs the wobble signal WB while increasing the frequencythereof as the laser position moves from the inner zone (Z0) to theouter zone (Zn). This allows the wobble signal generating circuit 7 togenerate a signal which will wobble the laser beam position at 397cycles per sector, regardless of the radial position of the beam.

In the address area (header area) AR2, a length corresponding to fivecycles of groove is allocated. A groove is formed to wobble in 3573cycles per track of the innermost zone Z0, and grooves are formed towobble in increments of 397 cycles per sector in general. In thisembodiment, 25 bytes of data per cycle are allocated to the user areaAR1 and one cycle occupies a length of about 42 μm.

The address signal generating circuit 6, under control of the systemcontrol circuit, generates and outputs an address signal SA whose valuechanges according to the movement of the optical head 4. That is, theaddress signal generating circuit 6 receives from the spindle motor 3 orthe like a timing signal (FG) that is synchronous with the rotation ofthe source disk 2, and counts the timing signal with a predeterminedcounter. With the counter information, the address signal generatingcircuit 6 generates address data corresponding to the laser beamirradiation position as shown in FIG. 3 (FIGS. 3(A), (C1), and (C2)).The numbers shown in FIG. 3 indicate the number of bytes of individualdata.

The address data is identified by an address data ID. A sector mark SM,timing data VFOs for synchronization, address marks AMs, and post amblePA are added to the address data ID, and the address signal generatingcircuit 6 generates a sector header to be allocated to each of the firsthalf and the second half of address area AR2 (FIGS. 3(B), (C1), and(C2)). The address signal generating circuit 6 forms each sector headerwith 62 bytes. (Up to 8K bytes of data may be recorded in the addressarea AF2.) The sector mark SM is allocated 4 bytes to indicate thebeginning of a sector header. Timing data VFOs for synchronization, usedto lock a PLL circuit in an optical disk recorder/reproducer, areallocated 26 bytes and 16 bytes respectively from the beginning of theheader.

Address mark AM is a one-byte address synchronizing signal. Address dataID consists of 6 bytes, two of which contain an error detection code.Two identical address data IDs are repeatedly recorded to increasereliability. Post amble PA (1 byte) is placed to set the polarity ofsignal.

The address signal generating circuit 6 converts a sector header thusgenerated into a serial data train and modulates it in a predeterminedformat. The modulated signal is output as address signal SAcorresponding to the scan position of the laser beam L.

A synthesizing circuit 8 uses the wobble signal WB and the addresssignal SA to generate a drive signal SD, the drive signal including ashift signal for shifting the position of the optical head 4 and a lightquantity control signal for controlling the light quantity emanatingfrom the laser beam. The drive signal SD is passed to the drive circuit5.

Accordingly, optical disks produced from the source disk 2 arepreformatted so that the information recording surface is concentricallysplit and the number of sectors increases in order from the inner zonesto outer zones. The address area AR2 is formed in the beginning of eachsector, the address of a following groove sector and the address of afollowing land sector are recorded in the address area AR2, and requireddata is recorded in the following user area AR1.

In this embodiment, the user area AR1 (FIG. 3B) includes a 24-byte guardarea following an 8-byte gap, a 25-byte VFO, a 2-byte synchronous area,a 9672-byte user data area, a 1-byte post amble (PA), a 52-byte guardarea, and a 16-byte buffer.

The gap area is provided to facilitate switching between a land and agroove and switching laser beam light quantity, and the guard area isallocated to suppress the fluidity of the recording medium caused byoverwrite and to improve the overwrite cycle of the recording area whenphase change media are used as the recording media. The synchronous byteis placed to lock a PLL circuit in an optical disk recorder/reproducer,the post amble is placed to set polarity, and the buffer is a redundantarea for eliminating jitter due to eccentricity or the like.

FIG. 4 is a perspective view showing an optical disk produced from thesource disk 2 and a sectional view of a groove. The optical disk has athickness of 1.2 mm. In the case of a phase change optical disk, thedisk includes the following ordered layers: an aluminum film, a ZnS-SiO2film, a GeSbTe film, and a ZnS-SiO2 film to produce an informationrecording surface. In the case of a magneto-optical disk, the diskincludes the following ordered layers: an aluminum film, an SiN film, aTbFeCo film, and an SiN film to produce an information recordingsurface. In the case of a write-once optical disk, the disk includes thefollowing ordered layers: an aluminum or gold sputter film and anorganic pigment film to produce an information recording surface.

Further, superimposed on the information recording surface is a lighttransmission surface of about 0.1 mm thickness, through which the laserbeam is transmitted and directed to the information recording surface.Using an optical disk according to this embodiment, the effects of lightskew can be minimized and therefore when the disk is exposed to a laserbeam of an optical system with a high numerical aperture, correctrecording and reproducing of data on the information recording surfacecan be realized.

The optical disk is formed having a radius of 60 mm with the arealocated between the radii of 24 mm and 58 mm being allocated forrecording.

Further, the optical disk is housed in a cartridge formed so as to becapable of identifying the type of optical disk. The disk and cartridgecan be integrally loaded into an optical disk apparatus, therebyreducing interference due to dust or the like during access by theoptical system with high numerical aperture.

With these arrangements, phase change optical disks are formed so thatdata can be recorded in such a way that the crystal structure of theinformation recording surface is locally changed through exposure to alaser beam, and so that recorded data can be reproduced by detecting achange in the quantity of reflected light.

Magneto-optical disks are formed so that data can be thermomagneticallyrecorded by applying a magnetic field at a laser beam irradiationposition, and so that data recorded through the Kerr effect can bereproduced by detecting the polarized surface of reflected light.Further, write-once optical disks are formed so that data can berecorded in such a way that the information recording surface isirreversibly altered by exposure to a laser beam, and so that recordeddata can be reproduced by detecting a change in the quantity ofreflected light.

As mentioned above, the source disk 2 is rotationally driven at aconstant angular velocity regardless of the radial position of the beam,the frequency of the wobble signal is varied according to the radialposition, and grooves are formed according to the wobble signal. As aresult, the wobbling cycle of the grooves is constant relative to theirradial position.

FIG. 5 is a block diagram depicting the wobble signal processing systemof an optical disk apparatus according to the invention. In the opticaldisk apparatus 10, a laser beam is irradiated from an optical head 11onto an optical disk 12 and the light reflected from the disk isdetected.

As shown in FIG. 6, in the optical head 11, semiconductor laser 13 isdriven by drive signal SL and irradiates a laser beam of 650 nm inwavelength. During reproduction, the quantity of light irradiated by thesemiconductor laser 13 is constant. On the other hand, during recording,the quantity of light irradiated is increased intermittently so as toform the pits (or "marks") required for recording information on opticaldisk 12.

A collimator lens 14 converts the laser beam emitted from thesemiconductor laser 13 into a parallel light beam and a shaping lens 15corrects the astigmatism of the beam. The beam then passes through abeam splitter 16 and objective lens 17.

The objective lens 17 directs the laser beam onto the informationrecording surface of the optical disk 12 and directs reflected lighttoward beam splitter 16. When reproducing, the optical disk apparatus 10is adapted to reproduce data recorded on optical disk 12 in response tochanges in the quantity of the reflected light. When the optical disk 12is a phase change optical disk, the optical disk apparatus 10 is adaptedfor recording data by changing the crystal structure of the disk at theposition of the impinging laser beam, and data thus recorded can bereproduced in response to changes in the quantity of reflected light.

Further, when the optical disk 12 is a write-once optical disk, theoptical disk apparatus 10 is adapted to record data by irreversiblyaltering the surface of the disk at the laser beam positions. As before,data can be reproduced in response to changes in the quantity ofreflected light.

On the other hand, when the optical disk 12 is a magneto-optical disk,the optical disk apparatus 10 is adapted so that data can be recordedthrough application of a thermomagnetic recording method. Morespecifically, data can be recorded by driving modulating coils 18disposed close to the objective lens 17 through a drive circuit 19, amodulated magnetic field can be applied to the laser beam irradiationposition. Data can be reproduced by detecting a change in the polarizedsurface of a reflected light.

In the configuration of FIG. 6, the beam splitter 16 allows a laser beamfrom shaping lens 15 to travel to the objective lens 17, while itreflects light from objective lens 17 to a beam splitter 20.

The beam splitter 20 allows some of the reflected light to pass andreflects the other remaining light to a lens 21, thereby separating thereflected light into two light beams.

Lens 21 converges light received from splitter 20 and directs theconverged beam to a cylindrical lens 22, which applies astigmatism tothe converged beam. A photodetector 23 receives the light emitted fromthe cylindrical lens 22.

The photodetector 23, the light-receptive surface of which is split intopredetermined light receptive surfaces, is adapted to be capable ofoutputting a light reception result for each light-receptive surface.The photodetector 23 subjects the light reception result of eachlight-receptive surface to current-voltage conversion by acurrent-voltage conversion circuit (not shown), and then performsaddition/subtraction operations by a matrix circuit. Thereby,photodetector 23 detects a reproduction signal RF whose signal levelchanges according to the quantity of reflected light, a push-pull signalPP whose signal level changes according to a shift of laser beamirradiation position for a groove or pit train, or a focus error signalFE whose signal level changes according to a defocus quantity.

Reflected light passing through the beam splitter 20 is passed to ahalf-wave plate 25 which changes the polarization of the light so thatit can be correctly separated by a polarized beam splitter 27 (describedbelow). A lens 26 converts the light emitted from the half-wave plate 25into a converged beam. The polarized beam splitter 27 receives theconverged beam, and reflects predetermined polarized components of thebeam and allows the rest to pass, thereby separating the incoming beaminto two beams whose relative light quantity changes according to thepolarization of the incoming beam.

Photodetectors 28 and 29 respectively receive the two light beamsgenerated by the polarized beam splitter 27 and each outputs a lightreception results which changes according to the quantity of receivedlight. A differential amplifier 30 receives the light reception resultsof the two photodetectors 28 and 29 via the current-voltage conversioncircuit and generates the differential amplification result, therebyoutputting a reproduction signal MO whose signal level changes accordingto the polarization of the light incident on splitter 27.

With these arrangements, the optical head 11 is adapted to record dataon a variety of optical disks 12 and to reproduce the recorded datatherefrom.

FIG. 7 is a sectional view showing a configuration of the objective lens17 of the optical head 11. The objective lens 17 comprises a first lens17A and a second lens 17B. The first lens 17A and second lens 17B, bothbeing formed as aspheric plastic lenses, are integrally supported byholding member 17C, and may be moved both perpendicular and parallel tothe disk by a drive actuator 17D. In this manner, the optical diskapparatus 10 can carry out tracking control and focus control byintegrally moving the first lens 17A and second lens 17B.

Further, the second lens 17B at the laser beam incoming side is formedwith a relatively large diameter, while the first lens 17A at theoptical disk side is formed with a small diameter, and the focaldistance of lens 17A, the focal distance of lens 17B, and the spacetherebetween are defined to set the numerical aperture of the objectivelens 17 to about 0.78

For this reason, the objective lens 17 is adapted to satisfy thefollowing relation; wherein: λ is the wavelength of the laser beam, NAis the numerical aperture of the objective lens 17, t is the thicknessof the light transmission layer of the optical disk 12, and Δt is thedispersion corresponding to t, and θ is the skew margin of the opticaldisk 12.

    θ≦±84.115×(λ/NA.sup.3 /t)     (2)

    Δt≦±5.26×λ/NA.sup.4 [μm]   (3)

The expression (2) shows the relationship between a skew margin θensuring stable access to an optical disk and the optical system(Japanese Unexamined Patent Publication 3-225650). Presentlymass-manufactured compact disks whose skew margin θ is about 0.6 degreesare commercially available. In DVD, skew margin θ is about 0.4 degrees.According to this embodiment, even though the thickness of the lighttransmission layer of optical disk 12 is about 0.1 mm and the numericalaperture NA of the optical system is about 0.78, practically stableaccess can be made to the optical disk 12.

The expression (3) shows the dispersion of the light transmission layer(thickness "t") permissible for the optical system. The constant 0.526is a value calculated with respect to the compact disk, and Δt is ±100μm for a compact disk and ±30 μm for DVD. For this reason, the opticaldisk apparatus 10 can gain stable access to the optical disk 12regardless of the dispersion of the thickness t of the lighttransmission layer.

By irradiating with a laser beam having a wavelength of 650 nm via theoptical system with a numerical aperture of 0.78, the optical head 11 isadapted to satisfy the following expression.

    Capacity≈4.7×[0.65/0.60×NA/λ].sup.2(4)

The number 4.7 is the recording capacity [GB] of DVD, and the numbers0.65 and 0.6 are the wavelength of laser beam in DVD and the numericalaperture of the DVD optical system, respectively. Accordingly, theoptical head 11 is adapted for a recording capacity of about 8 GB whendata processing is performed in the same manner as that of DVD.

In the objective lens 17 thus formed, the first lens 17A is supported inprotrusion toward the optical disk 12, thereby providing the workingdistance DW required by the numerical aperture. The working distance DWis set to about 560 μm in consideration of the characteristics andplacement of the first lens 17A and second lens 17B. Further, theoptical head 11 is constructed so that eccentricity tolerance (betweenthe lens faces of the objective lens 17), the face angle tolerance, andlens curvature are set in a range which is easily achieved in massproduction. The head is designed to be compact, and to avoid collisionwith an optical disk.

If the numerical aperture is increased for a given beam diameter, theobjective lens must be positioned closer to the information recordingsurface of the disk. Accordingly, sufficient space between the head anddisk, the beam diameter would have to be significantly increased.However, a practical upper limit on the beam diameter is about 4.5 mm,almost equal to that used in DVD.

On the other hand, to position an optical head close to an optical diskand reduce the beam diameter requires a high degree of precision inobjective lens fabrication and positioning. Otherwise, the optical headmay collide with the disk. In view of the above considerations, theworking distance DW in this embodiment is set to about 560 μm.

Further, the lens face of the first lens 17A toward the optical disk 12is flattened, thereby ensuring focus control and preventing collisionwith the surface of the light transmission layer if the optical disk isskewed.

The diameter of objective lens 17 is decreased in stages as the distanceto the disk decreases, and the diameter of the lens which faces theoptical disk 12 is made small enough to effectively direct a laser beamonto the disk 12.

Modulating coils 18 are positioned so that they surround the tip of thefirst lens 17A and as close to the optical disk 12 as possible--so longas they do not protrude from the lens face of first lens 17A. Notingthat the disk is almost parallel with the face of lens 17A, the coilsare capable of efficiently applying a modulated magnetic field to thelaser beam irradiation position.

A rise in the temperature of the modulating coils 18 is suppressed byradiation plates 17E positioned to surround the first lens 17A such thatvarious characteristic changes due to temperature rise can be restrictedto a practical range.

In the optical disk apparatus (FIG. 5), the spindle motor 33rotationally drives the optical disk under control of a system controlcircuit 34. In one implementation, the spindle motor 33 rotationallydrives the optical disk 12 by the so-called ZCLV (Zone Constant LinearVelocity) method so that a read/write clock (R/W CK) generated in PLLcircuit 35 becomes a constant frequency. (Zoning in relation to the ZCLVdescribed here corresponds to zoning as explained with respect to FIG.1.)

A sled motor 36 moves the optical head 11 radially with respect to theoptical disk 12 under control of the system control circuit. In thisway, the optical disk apparatus can carry out a seek operation.

An address detection circuit 37 receives a reproduction signal RF whosesignal level changes according to the quantity of reflected lightdetected by the optical head 11, and binary-codes the reproductionsignal RF. The address detection circuit 37 further detects an addressdata ID with reference to a synchronizing signal assigned to a sectorheader from the binary-coded signal and outputs it to the system controlcircuit 34. The detected timing is passed to a cluster counter 38.Accordingly, the optical disk apparatus 10 can locate the laser beamirradiation position based on the address data ID preformatted in theoptical disk 12 and passed to the system control circuit 34, and cancheck sector timing in the cluster counter 38.

Further, the address detection circuit 37, when outputting the addressdata ID, performs error detection processing through an error detectioncode assigned to each address data ID, and selectively outputs anaddress ID determined as valid.

A wobble signal detection circuit 39 delivers a push-pull signal PPoutputted from the optical head 11 to a band-pass filter 39A, whichextracts a wobble signal WB. The wobble signal detection circuit 39binary-codes the wobble signal WB with reference to 0 level in acomparator (COM) 39B, thereby extracting the edge information of thewobble signal WB.

A wobbling cycle detection circuit 40 receives the binary coded signalS1 and determines the wobbling cycle from the edge frequency (asdetermined from the edge information). The wobbling cycle detectioncircuit 40 outputs edge information to the PLL circuit 35 when it isdetermined that the wobbling cycle corresponding to that edgeinformation is correct. In this way, the wobbling cycle detectioncircuit 40 prevents clock errors caused by dust or the like deposited onthe optical disk 12.

The PLL circuit 35 delivers a binary-coded signal outputted from thewobbling cycle detection circuit 40 to a phase comparator (PC) 35A,which compares it with the clock CK outputted from a frequency dividingcircuit 35B. The divisor used by the frequency dividing circuit 35B isset according to the setting of the system control circuit 34. Thefrequency dividing circuit outputs a proper clock CK.

The PLL circuit 35, by means of a low pass filter (LPF) 35C, extracts alow frequency component from a phase comparison result outputted fromthe phase comparator 35A and controls the oscillation frequency of avoltage control type oscillating circuit (VCO) 36D by the low frequencycomponent. Further, the oscillation output of the voltage control typeoscillating circuit 36D is frequency-divided by the frequency dividingcircuit 35B, thereby generating a high precision clock CK.

In the PLL circuit 35, the frequency dividing circuit 35B is set by thesystem control circuit 34 so that the divisor increases as laser beamirradiation position shifts toward the outermost circumference of theoptical disk 12. With this arrangement, as the laser beam irradiationposition shifts toward the outermost circumference of the optical disk12, the frequency of oscillation output by the voltage control typeoscillating circuit 36D increases. In addition, the VCO output is usedas a read/write clock R/W CK.

In the optical disk apparatus 10, the optical disk 12 is rotationallydriven by the spindle motor so as to keep the read/write clock R/W CK ata constant frequency, and data is recorded based on the read/write clockR/W CK, the recording density is adjusted so as to prevent anysignificant difference of linear recording density between inner andouter circumferences.

Cluster counter 38 counts the read/write clock R/W CK cycles based onthe detection result of the address detection circuit 37, therebyallowing for highly accurate location of the laser beam irradiationposition. Further, the cluster counter 38 outputs a cluster start pulseto the system control circuit 34 based on the count result. The clusterreferred to here is a unit of recording/reproducing data for the opticaldisk 12, and a cluster start pulse is a pulse indicating the start timeof a cluster.

When a sector start timing is not detected by the address detectioncircuit 37 due to dust or the like on the disk surface, the system caninterpolate a cluster start pulse by synchronous processing based on theresult of counting the read/write clock R/W CK.

The system control circuit 34, which may be a computer controlling theoverall operation of the optical disk apparatus 10, for example,controls the operation of the sled motor and other components usingaddress data IDs, the laser beam irradiation position, and controlsignals from external equipment.

One of the processes carried out by the system control circuit 34 is toswitch the divisor used by the frequency dividing circuit 35B inresponse to the laser beam irradiation position. The various divisorsthat may be used can be stored in the memory 42.

With this arrangement, the system control circuit 34 decreases therotation speed of the optical disk in stages from the innermost zone tothe outermost zone, correspondingly to the zones Z0, Z1 . . . Zn-1, Zndescribed in FIG. 1, thereby setting the sectors on the inner and outerzones to an equal recording density.

By performing write/read control according to a cluster start pulseoutputted from the cluster counter 38, data of one cluster is assignedto four successive sectors, relative to address area AR2 allocated ineach sector. In this way, the system control circuit 34 increases thenumber of clusters assigned to zones in order from the innermost zone tothe outermost zone.

Further, the system control circuit 34 commands a tracking servo circuit(not shown) to move the objective lens 17 in response to the polarity ofa tracking error signal, and to switch the laser beam scanning positionbetween grooves and lands. This enables the optical disk apparatus 10 toperform the so-called land/groove recording.

FIG. 8 is a block diagram showing a recording/reproducing system of theoptical disk apparatus 10. In the optical disk apparatus 10, a diskdiscriminator 50 discriminates the type of optical disk 12 by detectinga depression formed in the disk cartridge, for example, and outputs adiscriminating signal to the system control circuit 34. Accordingly,different types of disks can be accessed by switching the operation ofthe recording/reproducing system in response to the type of loadedoptical disk 12.

An encoder 51 receives an input signal SIN which includes a video signaland an audio signal (e.g., from external equipment during recording orediting). The encoder subjects the video signal and audio signal toanalog-digital conversion processing, and then compresses the dataaccording to the MPEG (Moving Picture Experts Group) standard in orderto generate user data DU.

During reproducing or editing, a decoder 52 expands the user data DUoutputted from a recording/reproducing circuit 53 according to the MPEGstandard in order to generate digital video and digital audio signals,and converts the digital signals into analog signals SOUT.

The recording/reproducing circuit 53 accumulates user data DU outputtedfrom the encoder 51 during recording or editing, processes it inpredetermined block units, and records it on the optical disk 12.

As shown in FIG. 9, the recording/reproducing circuit 53 successivelydivides the user data DU into blocks of 2048 bytes each and adds 16-byteaddress data and error detection code to each block. Therecording/reproducing circuit 53 forms a sector data block with 2048plus 16 bytes. Address data contains the address of the sector datablock. Sectors containing the user data DU are different from thepreformatted sectors described above with respect to FIG. 1. An errordetection code is generated for the address data.

As shown in FIG. 10, the recording/reproducing circuit 53 forms an ECCdata block (182 bytes×208 bytes) with 16 sector data blocks. That is,the recording/reproducing circuit 53, as shown in the figure,successively arranges the 16 sector data blocks of 2048+16 bytes in theorder of raster scanning in units of 172 bytes, and generates an innererror correction code (PI) in the horizontal direction and an outererror correction code (PO) in the vertical direction.

The recording/reproducing circuit 53 subjects the ECC block tointerleaving and forms a frame structure shown in FIG. 11. That is, therecording/reproducing circuit 53 assigns a 2-byte frame synchronizingsignal (FS) to each 91 bytes of the FCC block of 182×208 bytes, therebyforming 208 frames for one FCC data block. In this way, therecording/reproducing circuit 53 forms one cluster of data according tothe frame structure shown in FIG. 11 and assigns the cluster to foursuccessive sectors.

The recording/reproducing circuit 53 assigns predetermined data of fixedvalue as required, and processes continuous data according to the sectorstructure described above with respect to FIG. 3. Further, therecording/reproducing circuit 53 subjects data strings to (1, 7) RLLmodulation, then outputs a data string after performing an operation onsuccessive bit strings. The data string is outputted at a data transferrate of 11.08 Mbps, so that it is intermittently output at a transferrate that is greater than the rate at which user data DU is inputtedfrom the encoder 51. As a result, the recording/reproducing circuit 53can record continuous user data DU without a pause.

During the data recording, the recording/reproducing circuit 53 outputsdata modulated on the basis of the read/write clock R/W CK describedabove with respect to FIG. 5, and starts to output data modulated on thebasis of the timing detected in the cluster counter 38 under control ofthe system control circuit 34.

Further, after amplifying signals RF and MO inputted from the opticalhead 11 during reproducing, the recording/reproducing circuit 53binary-codes them to generate binary-coded signals, and reproduces aclock from the resulting binary-coded signals. The clock thus reproducedcorresponds to the read/write clock R/W CK. Further, by successivelylatching the binary-coded signals on the basis of the reproduced clock,reproduction data is detected.

The recording/reproducing circuit 53 applies the PRML (Partial-ResponseMaximum-Likelihood) method to decode the reproduction data and generatedecoded data. Also, the recording/reproducing circuit 53 subjects thedecoded data to deinterleaving and error correction processing prior topassing the data to the decoder 52.

In DVD, data subjected to (1, 7) RLL modulation may be recorded with abit length of 0.4 μm. If a recording/reproducing system is formedaccording to the same margin as that of DVD (on a numerical aperturebasis), data can be recorded or reproduced with a bit length of 0.3 μmand a linear recording density of 0.23 μm/bit. On the other hand, byactively using intercede interference by PRML, the same margin could beobtained with a linear recording density of 0.23 μm or less.

At this time, in the same way as during recording, therecording/reproducing circuit 53 intermittently reproduces data from theoptical disk 12 in units of clusters at a data transfer rate of 11.08Mbps and continuously outputs the reproduced user data DU to the decoder52.

In reproduction processing, the recording/reproducing circuit 53, whenthe optical disk 12 is a magneto-optical disk, selectively processes theMO signal (level changes according to the polarized surface) undercontrol of the system control circuit 34, and reproduces user data DU.When the optical disk is a reproduction only, write-once, or phasechange optical disk, the recording/reproducing circuit 53 selectivelyprocesses the RF signal (level changes according to a change in thequantity of reflected light), and reproduces user data DU. When theoptical disk 12 is a magneto-optical disk, the recording/reproducingcircuit 53 selectively selects the reproduction signal RF and reproducesuser data DU when a read-in area at the inner circumferential side isreproduced.

The address read circuit 55, during recording, generates address data tobe added to each sector data block (FIG. 9) and outputs it to therecording/reproducing circuit 53, and during reproducing, analyzesaddress data detected in the recording/reproducing circuit 53 andreports the result to the system control circuit 34.

The modulating coil driving circuit 56, during writing, when the opticaldisk 12 is a magneto-optical disk, drives the semiconductor laser of theoptical head 11 in sync with the read/write clock R/W CK under controlof the system control circuit 34, intermittently increasing the lightquantity of a laser beam.

The laser driving circuit 57, during writing, when the optical disk 12is a phase change or write-once disk, intermittently increases the lightquantity of the laser beam according to the output data of therecording/reproducing circuit 53, thereby recording user data DU on theoptical disk 12.

On the other hand, the laser driving circuit 57 keeps the light quantityof the laser beam at a constant low level during reading.

The modulating coil driving circuit 56, when the optical disk is amagneto-optical disk, starts up recording operation under control of thesystem control circuit 34 and drives the modulating coil of the opticalhead 11 according to the output data of the recording/reproducingcircuit 53. The modulating coil driving circuit 56 applies a modulatedmagnetic field to the laser beam irradiation position as the lightquantity of the beam intermittently increases, and records user data DUby the thermomagnetic recording method.

FIG. 12 is a schematic diagram showing access to the optical disk 12when continuous data is recorded or reproduced under control of thesystem control circuit 34. The system control circuit 34 switches anaccess target from inner zones to outer zones based on address data IDdetected by the address detection circuit 37, and successively recordsor reproduces continuous data.

When the system control circuit 34 accesses data in a zone Zm, itcontrols the overall operation so that, after access is started at theinnermost groove of the zone (symbol G1), the groove track is accessedup to the outermost circumference of the zone Zm (symbol G2). Then, thesystem control circuit 34 issues a track jump command as shown by thesymbol J to switch the access target to the land track of the innermostcircumference of the zone Zm and controls the overall operation so as toaccess the land track from the innermost circumference (symbol L1) tothe outermost circumference (symbol L2) of the zone Zm.

With this arrangement, the system control circuit 34 drives the opticaldisk 12 by ZCLV in a manner that records continuous user data DU in arange in which a constant rotation speed is maintained, and records theuser data in a following outer area when recording in that range becomesdifficult. Accordingly, in the optical disk apparatus 10, the rotationspeed of the optical disk 12 is switched with less frequency so thataccess speed is improved.

The system control circuit 34 first records the user data DU in orderfrom the inner circumferential side to the outer circumferential sidewith respect to groove tracks in the range in which constant rotationspeed is maintained, and at completion of the recording, records theuser data DU in order with respect to land tracks, whereby the seekoperation of the optical disk 11 is also reduced so that access speed isimproved again.

Upon completion of such access to one zone, the system control circuit34 switches the access target to a following outer zone and starts torecord the continued user data DU on a groove track in the outer zone.Thus, the system control circuit 34 controls the overall operation so asto start access from a groove track in each zone.

In the above mentioned configuration, the mastering apparatus (FIG. 2)rotationally drives the source disk 2 and spirally irradiates the laserbeam L from the inner circumferential side to the outer circumferentialside of the disk, whereby grooves are formed at a space of about 1.0 μmand the groove shape is formed to wobble by a wobble signal WB.

Further, in the mastering apparatus, the spot shape and light quantityof the laser beam L are set so that the spaces between a groove formedby exposure of the laser beam L and adjacent grooves are almost equal,whereby an optical disk is formed so that land/groove recording can becarried out. In accordance with the invention, land/groove recording iscarried out at a linear recording density of about 0.21 μm/bit,(relative to grooves) so that 8 GB or more of data can be recorded.Accordingly, the mastering apparatus 1 is adapted so that 8 GB or moreof data can be recorded on optical disks produced from the source disk 2by making effective use of the information recording surface.

Zoning is carried out in such a way that the source disk 2 isrotationally driven under the condition of constant angular velocity andthe laser beam irradiation position is shifted by a wobble signal WBwhose frequency increases in stages. Thus, the wobbling cycle, which isbased on the basis of the rotation angle of the optical disk, is keptconstant between the inner and outer circumferences of each zone.

In the address signal generation circuit 6 of the mastering apparatus 1,an address data ID (FIG. 3(A)) whose value changes for each rotation ofthe source disk 2 is formed and data to be assigned to the address areaAR2 is formed with synchronous data, etc. appended to the address dataID (FIG. 1). The data, after being modulated, is synthesized with thewobbling signal WB in the synthesizing circuit 8, then is outputted tothe drive circuit 5. In this way, in the mastering apparatus 2, groovewobbling is stopped at a predetermined angular interval, address datarepresented by a pit train is recorded on the source disk 2, and sectorseach beginning with the address data are formed by spirally splittingthe source disk 2 at a predetermined angular interval.

In an optical disk produced from the source disk 2, access to thesectors on the basis of the address data can be correctly made byinterpolation processing based on groove wobbling even when address datacannot be correctly reproduced due to dust, etc. Accordingly,information can be recorded, as address data, at high density with lowredundancy, so that addresses recorded on the optical disk can becorrectly detected by making effective use of the information recordingsurface.

When a sector structure is formed in this way, the mastering apparatus 1concentrically zones the source disk 2 by varying the frequency of thewobbling signal WB and forms a pit train so that the number of sectorsincreases sequentially from inner zones to outer zones. As a result, theinformation recording surface can be effectively used by gaining accessto the optical disk through application of the zone CLV, and accessspeed can be improved.

The address area AR2 is divided into two areas, which are assigned theaddress data of a following groove sector and a following land sector,respectively, whereby, even when data is recorded at high density by theland/groove recording, crosstalk from adjacent tracks of address datacan be effectively avoided and the address data can be correctlyreproduced.

An error detection code is assigned to two bits of an address data IDand identical address data IDs are repeatedly assigned to one area, toprovide some redundancy and to reduce the likelihood that address datais incorrectly reproduced.

In the optical disk fabrication process according to this embodiment, anoptical disk is produced based on a sector structure formed on thesource disk 2 via a predetermined process implemented by the masteringapparatus 1.

The optical disk (FIG. 4) has an information recording layer coated witha light transmission layer of about 0.1 mm, through which the laser beamis transmitted and directed to the information recording layer. Thisconstruction allows correct recording/reproducing of data on/from theinformation recording surface by effectively avoiding degradation due toskew. The optical system which directs the laser beam through thetransmission layer has a high numerical aperture

The optical disk 12 is subjected to spindle control or other processingin the optical disk apparatus on the basis of the above-mentioned groovewobbling. In addition, the groove wobbling is used in the PLL circuit 35to generate a highly accurate clock Ck, and the clock is, in turn, usedby the cluster counter 35 (FIG. 6) to determine sector timing.

That is, the optical disk 12, in the optical disk apparatus 10 (FIGS. 5and 6), is irradiated by a laser beam of 650 nm in wavelength via anobjective lens having a numerical aperture of about 0.78 at a workingdistance of about 560 μm. The light reflected from the disk is receivedby the optical head 11, and the following signals may be detected: areproduction signal RF whose signal level changes according to the lightquantity of the reflected light, a reproduction signal MO whose signallevel changes according to the polarization of the reflected light, apush-pull signal PP whose signal level changes according to a shift ofthe position of laser beam irradiation onto a groove or pit train, and afocus error signal FE whose signal level changes according to a defocusquantity.

From the push-pull signal PP a wobble signal WB is extracted in thewobble signal detection circuit 39. The wobble signal WB is binary-codedand edge information is extracted. In the PLL circuit 35, a binary-codedsignal having the edge information is phase-synchronized with an outputsignal CK of the frequency dividing circuit 35B and the read/write clockR/W CK is generated.

Since the wobble signal WB is generated by a carrier signal of a singlefrequency, edge information resulting from the binary-coding operationcontains correct phase information. Accordingly, a read/write clock R/WCK having high accuracy is generated by synchronizing phases accordingto the edge information.

Further, the read/write clock R/W CK is counted by the cluster counter38 at a frame synchronization timing detected from the address area AR2in the address detection circuit 37. The information from the clustercounter is used to set the read/write timing in therecording/reproducing circuit 53 (FIG. 8). Since the system issynchronized by highly accurate clock R/W CK, the laser beam irradiationposition and write timing can be determined with high accuracy and theinformation recording surface of the disk can be used to record data ata high density.

Even when it is difficult to correctly detect frame synchronizationtiming in the address detection circuit 37 due to the influence of dust,etc. correct timing can be detected by counting the clock R/W CK

When the wobble signal WB is processed in this way, the frequencydivisor used in the PLL circuit 35 is varied according to laser beamirradiation position, thereby allowing ZCLV rotation of the disk.

Since the groove wobbling cycle is kept constant, the cycle of the PLLcircuit 35 is quickly recovered in each zone and access speed isimproved. Also, since the groove wobbling cycle is kept constant,wobbling signal degradation due to cross-talk can be effectivelyavoided.

In the optical disk apparatus 10 described above (FIG. 8), duringrecording, video and audio signals are subjected to data compression(e.g., MPEG encoding) in the encoder 51 and are converted into user dataDU, which is subjected to modulation processing in predetermined unitsof ECC blocks. Further, when the optical disk 12 is a magneto-opticaldisk, recording is carried out by intermittently increasing the beamintensity in synchronism with the read/write clock R/W CK and applying amodulated magnetic field according to the data of the ECC blockssubjected to modulation processing. The modulating coil driving circuit56 is used to apply the modulated field at the beam irradiationposition. In this manner, user data DU is thermomagnetically recorded.

To record when the optical disk 12 is a phase change or write-onceoptical disk, the quantity of laser beam light is varied by the laserdriving circuit 57 in accordance with the data of the ECC block and theread/write clock R/W CK.

In the optical disk apparatus 10, the user data DU of one ECC block issuccessively allocated to four sectors and recorded. Correct timing canbe insured by the highly accurate clock and the use of interpolation.Thus, sectors can be correctly recorded at a high density, on theoptical disk 12.

During reproduction, a particular sector is detected in the same way asit is detected during recording. After the reproduction signal RF or MO(obtained from the optical head 11) is binary-coded, a reproductionclock is generated and reproduction data is successively obtained basedon the reproduction clock. The reproduction data is decoded andoutputted. At this time, it should be noted that the reproduction signalMO obtained from the magneto-optical disk 12 has a smaller S/N ratio incomparison to the reproduction signal RF obtained from a pit train.Furthermore, it is noted that in this embodiment, since the address areaAR2 comprising pit trains is spirally formed in each zone, crosstalkfrom the pit trains to the reproduction signal MO is effectivelyavoided.

When accessing the optical disk 12 in this way, the optical diskapparatus 10, by the system control circuit 34 performing control basedon a sector address obtained from the optical disk 12 (FIG. 12), recordscontinuous user data DU in zone Zm where a constant rotation speed ismaintained by ZCLV, and records the user data DU in a following outerzone when recording in the zone Zm becomes difficult. Accordingly, inthe optical disk apparatus 10, the rotation speed of the optical disk 12is switched with less frequency so that access speed is improved.

In the zone Zm in which the constant rotation speed is maintained, userdata DU is first recorded in order from the inner circumferential sideto the outer circumferential side with respect to groove tracks, and atcompletion of the recording, the user data DU is recorded in the samemanner with respect to land tracks. Accordingly, in the optical diskapparatus 10, the seek operation of the optical disk 11 is also reduced,so that access speed is further improved.

According to the above mentioned configuration, the width of a grooveand that of a land are set to be almost equal. Grooves are formed on thedisk so that groove tracks and land tracks are alternately formed in aspiral fashion and the track pitch is set to 0.5 μm. The lighttransmission layer is set to a thickness of 100 μm. In the aboveconfiguration, information can be recorded at high density to provide anoptical disk system having a capacity of 8 GB.

In accordance with the invention, groove tracks and land tracks may beaccessed by irradiating a disk with a laser beam from an optical systemhaving a working distance of 560 μm and a numerical aperture of 0.78 ormore. The rotation speed of the optical disk is switched in stages fromthe inner circumferential side to the outer circumferential side of theoptical disk, to allow the recording density of the outercircumferential side to be set almost equal to that of the innercircumferential side, and to allow information to be recorded at highdensity by making effective use of the information recording surface.

Further, by serially accessing groove and land tracks respectively, andaccessing the innermost land track following the outermost groove trackin a zone in which the rotation speed of the optical disk is keptconstant, the rotation speed of the optical disk 12 can be switched withless frequency and the seek and access speeds can be improved.

FIG. 13 is a plan view showing access to an optical disk by an opticaldisk apparatus according to a second embodiment of this invention (incomparison with FIG. 12). In the second embodiment, the optical disk 12described above with respect to the first embodiment is accessed.

In the second embodiment, an optical disk apparatus accessing theoptical disk 12 is configured identically with the optical diskapparatus according to the first embodiment, except that the processingprocedure of the system control circuit in accessing the optical disk 12is different.

That is, according to this embodiment, when no data is recorded on theoptical disk 12, the system control circuit, when recording continuousdata on the optical disk 12, starts to record the data from theinnermost groove track (symbol G1) in the innermost zone Z0 of theoptical disk 12.

On completion of data recording on groove tracks in the zone Z0, thesystem control circuit starts to record the continuous data on groovetracks of a following zone Z1 as shown by the symbol G2, and repeats thedata recording on groove tracks up to the outermost zone Zn as shown bythe symbols G3 and G4.

On completion of access to the optical disk 12 up to the outermostgroove track in the outermost zone Zn, the system control circuit causesa jump to the innermost land track in the innermost zone Z0 (indicatedby jump track symbol J), and records the continuous data in order up tothe outermost land track of the optical disk, as shown by the symbols L1to L4.

Thus, in this second embodiment, the system control circuit reduces thetrack jump frequency with respect to the whole of the optical disk 12.

All of the advantages of the first embodiment can be realized whilereducing the track jump frequency with respect to the whole of theoptical disk 12.

FIG. 14 is a plan view showing an optical disk according to anotherembodiment of the present invention (in comparison with FIG. 1). In thefabricating process of an optical disk according to this embodiment,like the first embodiment, grooves are formed and the groove formationis stopped at a predetermined angular interval to record address data bya pit train. According to this embodiment, the address data of afollowing groove sector and the address data of a following land sectorare recorded in the first half and second half of address area AR2,respectively, and the pit train is placed on the center of a groovetrack.

The optical disk apparatus accesses the optical disk in the same way asin the above-mentioned embodiments.

All the advantages of the first embodiment may be realized in theconfiguration shown in FIG. 14.

FIG. 15 is a plan view showing an optical disk according to yet anotherembodiment of the present invention (in comparison with FIG. 1). In thefabricating process of an optical disk according to this embodiment,like the first embodiment, grooves are formed and the groove formationis stopped at a predetermined angular interval to record address data bya pit train. According to this embodiment, the address data of afollowing groove sector and the address data of a following land sectorare recorded in the first half and second half of address area AR2,respectively, and the pit trains in the first and second portions areformed on the boundaries of land and groove, respectively.

The optical disk apparatus accesses the optical disk in the same way asin the above mentioned embodiments.

All of the advantages of the first embodiment may be realized in theconfiguration shown in FIG. 15.

FIG. 16 is a plan view showing an optical disk according to a stillfurther embodiment of the present invention (in comparison with FIG. 1).In the fabricating process of an optical disk according to thisembodiment, tracks with a pitch of 0.5 μm are formed by alternatelyrepeating a groove and a land in a circumferential direction of anoptical disk in such a way that one round of a groove is followed by anouter land and one round of the land is followed by an outer groove.

Further, the groove formation is stopped at a predetermined angularinterval to record address data by a pit train. At this time, accordingto this embodiment, the address data of a following groove sector andthe address data of a following land sector are recorded on thecorresponding track center.

As shown in FIG. 17 in comparison with FIG. 12, in this embodiment, theoptical disk apparatus records continuous data by following tracks inorder from the inner circumferential side to the outer circumferentialside. When recording continuous data, the rotation speed of the opticaldisk is switched with less frequency and the seek time is reduced.

According to the configuration shown in FIGS. 16 and 17, when trackswith a pitch of 0.5 μm are formed by alternately repeating a groove anda land in a circumferential direction of an optical disk, the advantagesof the first embodiment can be realized, while a higher access speed isachieved compared to the first and second embodiments.

FIG. 18 is a plan view showing an optical disk according to anotherembodiment of the present invention (in comparison with FIG. 16). In thefabricating process of an optical disk according to this embodiment,grooves are formed in such a way that one round of a groove is followedby an outer land and one round of the land is followed by an outergroove. Further, the groove formation is stopped at a predeterminedangular interval to record address data by a pit train, the address databeing recorded in the first half and second half of address area AR2.The pit trains are placed on the boundaries of the groove and landrespectively, with an offset existing between the first and second halfportions.

The optical disk apparatus accesses the optical disk in the same way asin the last mentioned embodiment of FIG. 16.

The configuration shown in FIG. 18 can be applied to the land/grooverecording by alternate connection of a land and a groove, with the sameeffect as that in the last-mentioned embodiment of FIG. 16.

In the embodiments described above, 8K bytes of data are recorded as apit train in one address area AR2. However, this invention is notlimited to this; 2K- or 4K-byte data, for example, can be assigned.

In the embodiments described above, identical address IDs are repeatedtwice for recording. However, this invention is not limited to this;identical IDs can be repeated more than twice, or may not be repeated.

In the embodiments described above, grooves are wobbled by a wobblesignal that is not modulated. However, this invention is not limited tothis; the wobbling signal may be modulated so that the wobbled groovescontain information indicated by the modulation.

In the embodiments described above, the wobbling cycle of the grooves ischanged in stages corresponding to zones. However, the invention is notlimited to this, it can also apply to the case where the wobbling iskept constant regardless of the disk's angular velocity, the case wherethe wobbling cycle of the grooves is kept constant with respect tolinear velocity, and the case where the wobbling cycle of grooves on alinear velocity basis is changed in order in stages in a radialdirection of the optical disk.

In the embodiments of FIGS. 16 and 18 described above, the entire grooveis wobbled by a wobble signal. However, this invention, not limited tothis, it can also apply to the case where only one edge of a groove iswobbled, and the case where both edges of a groove are wobbled bydifferent wobble signals.

In the first to fifth embodiments described above, access is startedfrom a groove track. However, this invention is not limited to this;access may be started from a land track, or access may be started byalternately switching between land and groove tracks, depending on azone.

In the embodiments of FIGS. 1 to 16 described above, a pair of grooveand land tracks are spirally formed. However, this invention is notlimited to this; two or more pairs of groove and land tracks may bespirally formed.

In the embodiments of FIGS. 1 to 16 described above, one track isspirally formed by switching between a land and a groove each time atrack makes one round. However, this invention is not limited to this;one or more tracks may be spirally formed by switching between a landand a groove at a predetermined angular interval.

In the embodiments described above, grooves are formed by theland/groove recording so that a track pitch is 0.5 μm. However, theinvention is not limited to this, it can apply to the case where groovesare formed with a different track pitch. More specifically, a capacityof 8 GB can be obtained by setting the track pitch to 0.64 μm or less,depending on the linear recording density, the redundancy of data to berecorded, and the like.

In the embodiments described above, the thickness of the lighttransmission layer is set to 0.1 mm. However, this invention is notlimited to this; a capacity of 8 GB can be obtained by setting thethickness of the light transmission layer to 177 μm or less.Incidentally, the light transmission layer should have a thickness of atleast 10 μm.

In the embodiments described above, user data is recorded at a linearrecording density of 0.21 μm/bit. However, this invention, not limitedto this, it can apply to recording at a linear recording density of 0.23μm/bit while maintaining the same advantages as that in the abovementioned embodiments. When the linear recording density is representedin terms of bit length or mark length, the permissible shortest bitlength and shortest mark length are 0.3 μm.

In the embodiments described above, data is recorded or reproduced byirradiating a laser beam having a wavelength of 650 nm via an opticalsystem having a numerical aperture of 0.78. However, the invention isnot limited to this, it can apply to the case where data is recorded athigh density by an optical system having a higher numerical aperture.When the thickness of the light transmission layer and a practicableworking distance are taken into account, the same results as that in theabove mentioned embodiments can be obtained in the case of a numericalaperture of 0.78 or more and a working distance of 560 μm or less.

In the embodiments described above, the invention applies to recordableoptical disks. However, the invention is not limited to this, it canalso apply to reproduction only optical disks.

While the present invention has been particularly shown and described inconjunction with preferred embodiments thereof, it will be readilyappreciated by those of ordinary skill in the art that various changesmay be made without departing from the spirit and scope of theinvention. For example, although the invention has been described in thecontext of recording/reproducing on both lands and grooves, to implementthe invention in the context of recording on lands only, or in thecontext of recording on grooves only.

Therefore, it is intended that the appended claims be interpreted asincluding the embodiments described herein, the alternatives mentionedabove, and all equivalents thereto.

What is claimed is:
 1. A method for fabricating an optical storage disk,comprising the steps of:providing a base disk having a transparent layerand a recording layer, said transparent layer having a thickness between10 μm and 177 μm; and irradiating said base disk with a laser beam so asto form a multiple of recording tracks on said recording layer, saidtracks being substantially concentric about the center of said basedisk, having a track pitch of 0.64 μm or less, and alternating radiallybetween land tracks and groove tracks, wherein each land track islocated on the surface of said recording layer and each groove track islocated within a groove in said surface of said recording layer, andwherein said groove tracks are formed in a wobbled fashion according toa wobbling signal such that each said groove track is circular andsinusoidally shaped, and such that when said disk is rotated at asubstantially constant angular velocity said wobbling signal isincreased in frequency as the radial position of said beam moves towardthe outer edge of said disk and is decreased in frequency as the radialposition of said beam moves toward the inner portion of said disk sothat the wavelength of the sinusoid remains substantially constant withrespect to radial position on said disk.
 2. The method according toclaim 1, wherein the width of said land tracks is substantially equal tothe width of said groove tracks.
 3. The method according to claim 1,wherein only said groove tracks are allocated for the recording and/orreproducing of data.
 4. The method according to claim 1, wherein onlysaid land tracks are allocated for the recording and/or reproducing ofdata.
 5. The method according to claim 1, wherein said land tracks andsaid groove tracks are formed spirally about the center of said basedisk.
 6. The method according to claim 1, wherein:address data for atleast one of said recording tracks is recorded on said optical storagedisk; and said address data is located in an area of groovediscontinuity, said area being divided into two sections, a firstsection for storing groove address data and a second section for storingland address data.
 7. The method according to claim 6, wherein saidgroove address data is aligned with a groove track center and said landaddress data is aligned with a land track center.
 8. The methodaccording to claim 6, wherein said groove address data is aligned with agroove track center and said land address data is aligned with a groovetrack center.
 9. An optical storage disk, comprising:a transparent layerhaving a thickness between 10 μm and 177 μm; and a recording layerhaving disposed thereon a multiple of recording tracks, said tracksbeing substantially concentric about the center of said disk, having atrack pitch of 0.64 μm or less, and alternating radially between landtracks and groove tracks, wherein each land track is located on thesurface of said recording layer and each groove track is located withina groove in said surface of said recording layer, and wherein saidgroove tracks are formed in a wobbled fashion according to a wobblingsignal such that each said groove track is circular and sinusoidallyshaped, and such that when said disk is rotated at a substantiallyconstant angular velocity said wobbling signal is increased in frequencyas the radial position of said beam moves toward the outer edge of saiddisk and is decreased in frequency as the radial position of said beammoves toward the inner portion of said disk so that the wavelength ofthe sinusoid remains substantially constant with respect to radialposition on said disk.
 10. The disk according to claim 9, wherein thewidth of said land tracks is substantially equal to the width of saidgroove tracks.
 11. The disk according to claim 9, wherein only saidgroove tracks are allocated for the recording and/or reproducing ofdata.
 12. The disk according to claim 9, wherein only said land tracksare allocated for the recording and/or reproducing of data.
 13. The diskaccording to claim 9, wherein said land tracks and said groove tracksare formed spirally about the center of said disk.
 14. The diskaccording to claim 9, wherein:address data for at least one of saidrecording tracks is recorded on said optical storage disk; and saidaddress data is located in an area of groove discontinuity, said areabeing divided into two sections, a first section for storing grooveaddress data and a second section for storing land address data.
 15. Thedisk according to claim 14, wherein said groove address data is alignedwith a groove track center and said land address data is aligned with aland track center.
 16. The disk according to claim 14, wherein saidgroove address data is aligned with a groove track center and said landaddress data is aligned with a groove track center.